H∞ control system for a four-high stand rolling mill

AbstractIn steelworks the demand for a higher product quality level has improved the rolling mill process by means of a proper work roll speed control system. Firstly this paper proposes a lumped-parameter hot-rolling mill model. The rolling mill examined is reversible and equipped with an independent speed control system for each work roll (two single-input single-output systems). Therefore, the same revolution speed, essential for a high-quality process, can only be ensured by equal set point values. Nevertheless, during the process, different disturbance load torques cause speed differences and, even if they are not noticeable, rolled section defects cannot be avoided. The second part of the paper shows that it is possible to design a proper H∞ controller, to change the two independent control systems into a more complex multiple-input multiple-output system that will obtain decidedly better performances. Simulation examples have shown improvements.